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Honors 227 Fall 2008
Chapters 8 and 9Atoms and Quantum MechanicsPresented by Prof. Geller
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The Atom
Chapter 8
Great Idea:All of the matter around us is made of atoms, the chemical building blocks of
our world
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Chapter Outline
• The Smallest Pieces• The Structure of the Atom• When Matter Meets Light• The Periodic Table of the Elements
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The Smallest Pieces
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The Smallest Pieces• Democritus
–Cut matter to reach smallest piece–Called “the atom” or “uncuttable”–All material formed from atoms
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Elements
• John Dalton–Father of modern
atomic theory–Cannot break down
elements–Elements
composed of atoms• Example: Water
Molecule is 1 oxygen atom and 1 hydrogen atom
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iClicker Question
• Greek philosophers came up with the idea of “atom” which roughly translates as–A small–B uncuttable–C reactive
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iClicker Question
• An atom is–A the smallest representative
sample of water–B something that can be cut in half
and still be the same–C the smallest representative
sample of an element
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Are Atoms Real?
• Evidence for the reality of atoms–Behavior of a gas–Chemical combinations–Radioactivity–Brownian motion–X-ray crystallography–Atomic-scale microscopy
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The Behavior of a Gas
• Bernoulli – atoms have mass &
velocity and thus kinetic energy
• Decreasing volume increases pressure (A)
• Increasing temperature increases pressure (B)
Relationship between Volume and Pressure
Volume0 2 4 6 8 10 12 14
Pres
sure
(mm
Hg)
10
20
30
40
50
60
70
80
90
A
Relationship between Temperature and Pressure
Temperature220 240 260 280 300 320 340 360 380 400 420 440
Pres
sure
30
35
40
45
50
55
B
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Chemical Combinations
• Dalton applied law of definite proportions– Elements combine in a specific ratio of weights
• Ex: Water is 8 parts oxygen to 1 part hydrogen
• Ratio of weights is a small whole number– Ex: 12 lbs Carbon can combine with either 16
lbs or 32 lbs of oxygen
• Implication: some units of elements are fundamentally indivisible
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Radioactivity
• Radioactivity• Phosphors flash when hit by radiation• 1903 demonstrated the twinkling
caused by this effect
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Brownian Motion
• Brownian motion: erratic, jiggling motion–pollen grains suspended in water
• Einstein: motion is random collisions of atoms–Predicted particle movement
• Perrin tested and confirmed Einstein’s predictions
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X-ray Crystallography
• Developed in 1912• Demonstrates arrangement of atoms
in crystals
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Discovering Chemical Elements
• Electrolysis• Mendeleev• Current Periodic Table
– 112 elements• 92 found in nature
• Everyday elements– Helium, carbon,
aluminum, copper, gold
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iClicker Question
• Evidence for the atomic particulate nature of matter includes–A ratios of elements in chemical
combinations–B Brownian motion–C gas behavior–D all of the above
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iClicker Question
• Brownian motion is–A one of the evidences that matter
is atomic–B part of the atomic theory–C a famous experiment that Albert
Einstein and John Dalton worked on together
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The Structure of the Atom
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The Structure of the Atom
• Thomson identified electron–Negatively charged–Smaller and lighter than smallest atom
• Atoms are NOT fundmental building blocks, but are made up of smaller more fundamental particles
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The Atomic Nucleus
• Rutherford determined atomic structure
• Concluded– atom has nucleus at
center surrounded by electrons
• Later discoveries found nucleus is composed of protons and neutrons
Most particles traveled through foil
Some deflected
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Why the Rutherford Atom Couldn’t Work
• Why?–Object in circular orbit is accelerating–Accelerated electrical charge emits
electromagnetic radiation–Electrons giving off energy while
orbiting• Result: electrons spin toward nucleus
eventually atom ceases to exist
• Rutherford atom exists <1min
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iClicker Question
• Thomson identified a particle called the electron in 1897. This provided evidence that–A atoms are not fundamental
building blocks of matter–B atoms could not be subdivided–C atoms are fundamental building
blocks of matter
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iClicker Question
• The results from Rutherford’s experiment were:
– A most of the alpha particles scattered and a few alpha particles went straight through the foil
– B all of the alpha particles scattered– C most of the alpha particles went
straight through the foil and a few alpha particles scattered
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iClicker Question
• The conclusion from Rutherford’s experiment includes the concept that:
– A atoms have negative particles– B atoms are mostly empty space– C atoms have high density
throughout the atom
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When Matter Meets Light
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The Bohr Atom
• First working model of atom • Energy levels for electrons
–Specific distances from nucleus
–Electrons exist with no radiation
–Electrons cannot exist between allowed distances (energy levels)
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Example Figure 8-7
Lowest energy level
Any level above ground state
Energy changes when level changes
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Photons: Particles of Light
Used to move electron to higher energy state
Photon emitted as electron moves to lower energy state
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Photons cont.• Quantum leap or jump-electron
disappears from original location and reappears in final location-never at positions in between
Energy is equal
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Energy in Bohr atom
• Energy required to leave ground state–Absorb photon–Heat
• Increases collisions
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Spectroscopy
• Atoms emit and absorb different photons
• Depends on differences between energy levels
• Each atom has distinct set of photons• Spectrum: all photons emitted by an
atom–Used for identification
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Spectroscopy cont.
Light from gaseous atoms is spread out by passing through a prism
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Spectroscopy cont.Each atom produces a unique set of lines-the atomic fingerprint
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iClicker Question
• The development of atomic theory from Dalton, Thomson, Rutherford and Bohr shows that:
– A theories are continually refined as new data becomes available
– B scientists keep changing their minds
– C the scientific method does not work
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iClicker Question
• In the Bohr model of the atom, a quantum jump is:
– A when an electron makes a giant leap
– B when a photon leaps from electron to electron during energy absorbing and emitting processes
– C when an electron moves from one allowed state to another without ever being in between states
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iClicker Question
• The evidence supporting Bohr’s atomic theory (electrons can only be in certain allowed energy levels) is:
– A atomic line spectra– B nuclear radiation emitted by
atoms– C bombardment of gold foil
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iClicker Question
• Spectroscopy is:– A another name for lasers– B a tool used in almost every
branch of science– C a device for making eyeglasses
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The Periodic Table of the Elements
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Periodic Table of the Elements•Systematizes elements•Columns contain similar elements
soft, silvery elements
all colorless, odorless inert gases
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Why the Periodic Table Works: Electron Shells
• Patterns mirror arrangement of electrons in shells
• Pauli exclusion principle
• First shell 2 electrons, second shell 8 etc.
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iClicker Questioin
• The periodic table is arranged with the elements:
– A getting progressively heavier left to right and top to bottom
– B having random order– C getting progressively more
reactive left to right and top to bottom
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iClicker Question
• The periodic table “works” because:– A of the names of the families of
elements (alkali metals, noble gases, etc.)
– B of the Pauli exclusion principle– C the pattern of elements in the
periodic table mirrors the spatial arrangement of electrons into shells
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iClicker Question
• A chemical reaction involves:– A neutrons in the outermost shell– B protons in central shells– C electrons in the innermost shell– D electrons in the outermost shell
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iClicker Question
• Which of the following evidences for atoms is most convincing to you:
– A The behavior of gases– B chemical combinations– C radioactivity– D Brownian motion– E X-ray crystallography
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Quantum Mechanics
Chapter 9
Great Idea:At the subatomic scale, everything is
quantized. Any measurement at that scale significantly alters the object being
measured
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Chapter Outline
• The World of the Very Small• Probabilities• Wave-Particle Duality• Wave-Particle Duality and the Bohr
Atom
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The World of the Very Small
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The World of the Very Small
• Quantum mechanics–Motion of quanta
• Bundles vs. continuous• Does not match our intuition
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Measurement & Observation in the Quantum World
• 3 components to measurement–Sample–Source of energy–Detector
• Quantum World–Measurement
alters object
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iClicker Question
• A quantum leap is when:– A an electron leaps from a proton to
a neutron– B a giant leap is made by some
subatomic particle– C an electron moves between
energy levels and emits a photon
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iClicker Questions
• True or False: Everything comes in quantized bundles.
– A true– B false
• Quantum mechanics is the branch of science devoted to the study of:
– A the Doppler effect– B broken electronic devices– C imaging devices– D the motion of objects that come in
small bundles
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iClicker Questions
• Which three components are essential to every measurement in the physical world?
– A a sample, a quantum scale and a recorder– B a recorder, a detector and a computer– C a sample, a detector and a light source– D an imaging device, a recorder and a light source
• The fundamental difference between the quantum and macroscopic worlds is:
– A the objects are too small to detect in the quantum world
– B the objects are too fast to detect in the quantum world
– C any measurement at the quantum scale significantly alters the object being measured
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The Heisenberg Uncertainty Principle
• Uncertainty Principle:– At quantum scale, measurement alters object
• Cannot know position and velocity• Equation:
• Compare large vs. small objects– Small uncertainty with large object– Large uncertainty with small object
mhvx >ΔΔ *
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Probabilities
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Probabilities
• Newtonian View–Determine
velocity and position
• Quantum View–Cannot determine
velocity and position
–Use probability
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iClicker Question
• Heisenberg’s equation: Δχ x Δν > h/m, is a shorthand way of saying:
– A you can never know both the position and velocity of an object with perfect accuracy
– B you can know both the position and velocity of an object with perfect accuracy if given the mass
– C you can know both the position and velocity of an object with perfect accuracy if given an accurate value for Planck’s constant
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iClicker Questions
• We do not have to worry about the uncertainty principle in our everyday life because:
– A the value of Planck’s constant is very small for large objects
– B the small velocity of large objects makes the uncertainty principle invalid
– C for objects with significant mass, the effects of the uncertainty principle are totally negligible
• The uncertainty principle is only significant when applied to:
– A really large objects such as planets– B tiny objects such as protons and electrons– C medium objects such as bowling balls
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Wave Particle Duality
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The Double-Slit Test
• Energy–Particles–Waves
• Photons–Emit photon–Flood of photons
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Double-Slit cont.
• Single photon over time
• Results depend on experimental design
• Visualizing–Not wave or
particle
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Wave-Particle Duality and the Bohr Atom
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Wave-Particle Duality & the Bohr Atom
• Speed & Wavelength– Faster speed=shorter wavelength
• Particle– Precise velocity=stable orbit
• Wave– Uniform vibration at certain frequencies
• Combine wave & particle?– Only orbits allowed are those where both particle and
wave work
Wave length determines frequency
Bending wave into circular orbit, fit only certain standing waves into orbit
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iClicker Questions
• Wave mechanics” is another term for:– A people who repair wave generators– B study of ocean wave motion– C quantum mechanics
• A famous experiment used a double-slit apparatus to determine:
– A velocity of light– B mass of an electron– C whether something is a wave or a
particle
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iClicker Questions
• True or False: All quantum objects exhibit properties of both particles and waves.
– A True– B False
• When light strikes one side of a thin sheet of material, electrons can be observed coming out the other. This phenomenon is called:
– A Einstein’s quantum propulsion– B the photoelectric effect– C the Heisenberg particle observation
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Quantum Weirdness
• Richard Feynmann- “I can safely say that nobody understands quantum mechanics. …Do not keep saying to yourself, ‘But how can it be like that?’… Nobody knows how it can be like that.”
• Be Careful!–Quantum mechanics is still a marvelous
and necessary tool for understanding the quantum world
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Quantum Entanglement
• Quantum Entanglement–Dice
• Photons emitted at same time–Despite distance, remain entangled
• Quantum teleportation– Is the photon created the same as the
one that was destroyed?
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iClicker Questions
• True or False: a group in Vienna sent a picture through the use of quantum teleported photons
– True– False
• Quantum mechanics is being used by some scientists to understand the phenomenon of consciousness. Some have argued that:
– the brain is no more than a physical structure– the workings of the brain can be predicted, but only at
the quantum level– both a and b
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iClicker Question
• The idea that quantum objects behave so differently from objects in our everyday experience leads to a feeling that nature has become “weird” at the subatomic level. How does this make you feel?
– A worried– B interested– C confused– D don’t care